The present invention relates to a calorimeter and, more particularly, to a simple calorimeter wherein a thermal type flowmeter and a laminar flow-type flowmeter are serially connected to one another to detect a loss of pressure in the mixed fuel gas in a normal state at the outlet of said laminar flow-type flowmeter on the condition that the output of the thermal-type flowmeter is kept at a constant value and to determine the calorific value of the mixed fuel gas as a function of the lost pressure.
It is regulated by law that fuel gas and natural gas, before being forwarded from a manufacturing works, shall be measured for their calorific values and combustability, and that calorimeters to be used for measuring the calorific values of a mixed gas also shall comply with the specified requirements.
A typical example is the Junker's flow-type gas calorimeter which completely burns a sample of mixed fuel gas with air and then cools the combustion product (waste gas) to the initial temperature thereby bringing the by-produced water vapor into a liquid state and causing the total amount of generated heat to be absorbed by the water, thereby multiplying the current water flow to correspond to a certain amount of mixed gas sample by the difference between the temperatures of said water at its inlet and outlet in order to get a product from which a total calorific value is calculated. This calorimeter is used as a standard instrument, but in application it requires such severe surrounding conditions that the difference between the room's temperature and the water's temperature must be kept at the constant temperature of .+-.0.5.degree. C. and the change in the water's temperature during one measurement shall not be more than 0.05.degree. C. and, furthermore, there is a poor response time. Therefore, the calorimeter is suitable for accuracy tests but not suitable for use in a production line. Consequently, it is also possible to apply quick-response calorimeters which are normally used for continuously measuring calorific values of fuel gas products before being forwarded from the manufacturing works. The quick-response calorimeters are such that fuel gas and air are respectively measured and then mixed with one another, the mixture being burned by the use of a burner, the temperature of the waste gas produced and temperature of the air at the burner's inlet are detected respectively by the use of temperature sensors, e.g. by thermo-couples, the difference between the temperatures and the specific gravity of the fuel gas in relation to the air are detected respectively, the Woppe's index (hereinafter referred to as W.I) which is a ratio of a total calorific value of the sample gas to the square root of the specific gravity of the sample gas relative to air is calculated, the calorific value of the sample gas is determined as a product of the W.I. and the square root of the specific weight of the sample gas relative to air. Another measuring method is to calculate the calorific value of the mixed gas from the result of the measurement of its density based upon the results of experiments showing the proportional relation between the calorific value and the density of the mixed gas.
The above-mentioned quick-response type calorimeters, usable in place of the standard Junker's flow-type gas calorimeter, have the drawback that when they have been operating for a long time, the accuracy of the measurements is decreased thereby requiring the correction of the measured value to twice the continuous cycle of operation. This correction work is complicated and not easy to do. The drawback of the densitometric method is that since the applicable density meter is expensive, it is impossible to provide a low cost and simple means for measuring the calorific values of the fuel gas.